The present invention relates generally to light beam projectors and, more particularly, to a true pendulous compensator for use in such projectors wherein the compensator comprises a pulley system with a suspended pulley including a pendulum mirror secured to and movable with the suspended pulley for reflecting the light beam to compensate for tilting of the light beam projector.
Light beam, typically laser beam, systems are used in leveling, squaring and other alignment and control functions in the building and construction industries. When using light beam systems, it is important to be able to position a light beam source or projector such that the light emitted by the projector is maintained in a desired orientation for example horizontal or at a selected angle relative to horizontal. Since stable horizontal leveling of the projector may be difficult, particularly at a construction site, prior art light beam projectors have employed pendulous compensators to direct a vertically emanating light beam in a desired horizontal direction regardless of whether the projector is tilted and hence not absolutely horizontal.
A simplified schematic diagram of a laser beam projector 100 including a housing 102, a laser beam source 104, focusing lenses 106 and a conventional pendulous compensator 108 is shown in FIG. 1. The pendulous compensator 108 is shown as being mounted to a bracket 110 and comprising a pendulum arm 112 pivotally coupled to and suspended downwardly from the bracket 110 for pivotal movement within a plane perpendicular to a pivot axis 114 of the arm 112, and a beam reflecting mirror 116 fixedly attached to the lower end of the arm 112. The laser beam source 104 and the bracket 110 are fixedly attached to the housing 102 and aligned such that a laser beam 118 projected upwardly from the laser beam source 104 lies within the pivot plane of the arm 112 and preferably passes through the pivotal axis 114 of the pendulum arm 112 if the arm 112 and beam reflecting mirror 116 are removed.
When the projector 100 is placed in a true horizontal orientation, the laser beam 118 is emitted in a true vertical orientation and the pendulum arm 112, which in theory due to gravity always assumes a true vertical orientation, is aligned with the laser beam 118. The laser beam 118, which is first focused and collimated by the lenses 106, is reflected by the mirror 116 in the horizontal direction within the pivot plane of the pendulum arm 112. If the laser beam projector 100 becomes tilted away from horizontal, such tilting is compensated by the movement of the pendulum arm 112. However, if the pendulum arm 112 is freely movable about the axis 114, compensation errors result. Accordingly, a pair of counterbalancing springs 120 may be connected between the pendulum arm 112 and the housing 102 to correct the errors which would be created by true pendulous motion of the arm 112.
As seen in FIG. 2, the housing 102 and hence the laser beam 118 are oriented at an angle "a" relative to vertical. However, the pendulum arm 112 biased by the springs 120 is now displaced counterclockwise about the axis 114 from the line of emergence of the laser beam 118 through an angle "a/2" which compensates for the angular tilt of the housing 102. In accordance with known operating principles of the pendulous compensator 108, the laser beam 118 continues to be reflected by the mirror 116 substantially in the horizontal direction. As an alternative to the counterbalancing springs 120, the pendulum arm 112 can be cantilevered or fixedly mounted to the housing 102 with the arm 112 formed such that it bends or deflects to compensate for tilting movement of the projector 100.
Unfortunately, bearings for supporting the pivoting pendulous compensator 108 must not only precisely support the pendulum arm 112 but also permit the arm 112 to freely pivot under the forces of gravity and the springs 120. Such bearings tend to be either complex and thus expensive or inappropriately fragile such as knife-edge bearings and subject to damage in the rather harsh environment of a construction site. Further, friction within the bearings leads to errors in the corrected horizontal orientation of the laser beam 118 and creates hysteresis in the operation of the pendulous compensator 108. Selection and balancing of the springs 120 present additional problems particularly over extended time and when used in varying temperatures. Problems also are present in cantilevered pendulous compensators which tend to be nonlinear and are limited to correcting tilt angles of approximately 5.degree. or less.
Accordingly, there is a need for a true pendulous compensator for a light beam projector which compensates for a wide range of tilt angles of the projector by maintaining the projected beam of light horizontal or at a desired angular orientation relative to horizontal in spite of such tilt angles, does not require complex, expensive bearings and can tolerate the harsh environment typical of construction sites.